1. Field of the Invention
The present invention relates to a recovery system for restoring preserved regeneration data. More particularly, the present invention is concerned with a recovery system that restores data using a backup when a transmitter transmits, in real time, image data or the like to a receiver in the form of a packet and the data received by the receiver suffers an error or a loss.
2. Description of the Related Art
A transmitter-receiver system consists mainly of a transmitter that distributes data including image data and places data created in real time, or existing data, on a network, and a receiver that receives and regenerates the data stream. In the transmitter-receiver system, the receiver includes a data reception mechanism, a data regeneration mechanism that regenerates an output of the data reception mechanism, and a storage device in which the output of the data reception mechanism is preserved.
The receiver that gives priority to regeneration does not include a large-capacity intermediate buffer. This is intended to prevent the speed of received data from being delayed in a data flow transmitted from the transmitter while keeping a time stamp specified in a data stream transmitted therefrom. Moreover, the receiver does not issue a regeneration request to the transmitter despite the occurrence of a lost packet. When the receiver preserves data while regenerating other data, an error packet or data from which a packet has been lost may be preserved in the storage device included in the receiver, though it depends on the condition of a network or the performance of the receiver (the speed at which a hard disk is written or the capability of a CPU).
As for conventional recovery systems for restoring preserved regeneration data, for example, one described in Japanese Unexamined Patent Publication No. 10-70523 is well known. The publication disclosed an art that, when a transmitting side retransmits data, a receiving side indicates in the form of a bit map what packet has caused an error, and transmits the bit map to the transmitting side. Compared with a method in which a transmitting side follows a retransmission procedure every time an error packet is detected, the disclosed method proves efficient.
Moreover, a recovery system disclosed in Japanese Unexamined Patent Publication No. 10-308932 is also well known. The publication is analogous to Japanese Unexamined Patent Publication No. 10-70523. Namely, the publication has disclosed an art attempting to improve the efficiency in recognizing an error (in units of a block) and in retransmitting packets (in units of a block) by managing packets in units of a block, which is composed of a plurality of packets, at a receiving side.
According to the art disclosed in the Japanese Unexamined Patent Publication No. 10-70523, the efficiency in retransmission is improved. However, because of the inclusion of the retransmission procedure, when motion picture data is transmitted from a transmitting side to a receiving side, an event where part of the motion picture received by the receiving side is lost occurs. This poses a problem in that the motion picture may stop or become hard to view.
According to the art disclosed in the Japanese Unexamined Patent Publication No. 10-308932, similarly to the Japanese Unexamined Patent Publication No. 10-70523, when a transmitting side retransmits data, a motion picture received by a receiving side may temporarily stop.